Applicants claim priority of German Application Ser. No. 199 38 131.3 filed Aug. 16, 1999.
The invention relates to a fuel tank for a motor vehicle and, more particularly, to a fuel tank assembly which structurally accommodates a fuel pump module and/or a fuel filler pipe.
Presently, a fuel tank or container which is incorporated into a fuel tank assembly of an automotive vehicle may be made of plastic. Furthermore, due to increasingly strict regulations concerning the permeation and escape of fuel and fuel vapors from fuel containers, the structural design of the mounting connection between the fuel container and, for example, a fuel pump module or a fuel filler pipe is particularly critical. In the particular case of a fuel pump module, it is necessary that the fuel container includes an opening in its container wall for physically accommodating and structurally mounting the fuel pump module in the fuel container. More particularly, a cover element which is mounted in the opening of the fuel container carries an electric fuel pump module such that the cover element includes the connectors and conduits necessary for supplying electricity to the fuel pump and transferring (that is, pumping) fuel from the container to the engine. These structural parts may include, for example, a fuel pump, a fuel level indicator, and/or ducts or conduits for transferring fuel from the container and to the engine. In addition, it is also necessary that the fuel pump module be specifically mounted to the fuel container so as to be removable for service and repair purposes. To satisfy all the necessary requirements, various solutions have been proposed in the art.
In a first proposed solution, for example, threads are formed during a blow-molding process on a tubular portion which defines an opening in a plastic fuel container. A nut is engaged therewith for urging the cover element against the tubular portion. For sealing purposes, a sealing ring is inserted between the threads and the cover element during assembly. This solution, however, suffers from a plurality of drawbacks. First of all, manufacturing difficulties typically arise because the threaded portion must necessarily include a certain minimum number of supporting threads and, therefore, must extend relatively far beyond the fuel container wall. This may cause material flow problems during blow molding so that a uniform wall thickness of a threaded portion cannot be ensured. In addition, this may also damage the closure when it is subject to substantial loads so that fuel may leak from the container. Furthermore, the cost of assembly is also undesirably substantial because an assembly person has to tighten the nut with a precise, predetermined amount of applied torque. That is, on the one hand, the applied torque should not be too high in order not to damage the threaded portion of the nut. On the other hand, the applied torque should not be too small in order to ensure tightness and sealing of the closure. Nevertheless, even when assembly pursuant to this first solution is properly carried out, the torque and tightness of the nut eventually change over time due to aging. Furthermore, since the fuel container is situated within the vehicle at a location which is not easily accessible, tightness of the closure of the fuel system at such a location typically is neither properly monitored nor timely adjusted and, instead, is not monitored and is adjusted only if the fuel pump module is removed and serviced or replaced. As a result, undesired fuel permeation often occurs under this first solution.
In a second proposed solution, a metallic ring is inserted into the blow mold during the manufacturing process of a conventional closure system. In a further step of the blow molding process, the metallic ring is embedded in the material of the container. In this way, the metallic ring extends partially beyond the wall of the fuel container and thereby forms part of a bayonet joint. While this particular solution enables a relatively small assembly height, additional steps in the manufacturing process pursuant to this solution are undesirably required. Furthermore, such a proposed closure system also does not properly satisfy all safety requirements. For example, a fuel container according to such a proposed closure system may be subjected to an extremely high shock load during a car accident. Such a shock load may cause the interior pressure of the fuel container to increase abruptly, even though the container may be deformable to a certain extent. In light of such, the interior pressure resistance of a closure system is a feature which is important to safety. However, in this proposed closure system, it has been found that a sudden increase in the internal pressure may cause the sealing ring to be urged from its seat so that fuel may leak from the container. Another feature important to safety is the cold flow toughness of a closure system which is tested at a temperature of xe2x88x9240 degrees Celsius, and such a low temperature may result in brittleness of the closure system material. After testing, it was found that the closure system according to the second solution often failed this low-temperature test when thereafter being subjected to room temperature despite the great strength inherent in the closure system. In particular, the differences in stiffness and coefficients of thermal expansion between the metallic ring and the surrounding plastic material resulted in reduced deformation characteristics and eventually to the metallic ring being broken out of the container wall such that the fuel container was irrevocably damaged.
A modification of the above-described second solution consists of the metallic ring, first, being embedded in a separate plastic ring. Thereafter, the resulting ring unit is fixed to the container wall in the area of the opening by plastics welding after the container has been blow-molded. While this particular modification helps facilitate the blow molding method solution, the modification undesirably requires an additional step for mounting the unit comprising the metallic ring and the plastic ring. In addition, more space is required for implementing this modification. Furthermore, with regard to the internal pressure resistance and the cold flow resistance problems described above, these problems are still present even upon implementing this modification.
A third proposed solution, which offers good permeation resistance, involves implementing an injection molding process prior to the blow molding of the container. In the injection molding process, a metallic ring is enclosed, at least partially, by plastic material. The resulting pre-fabricated part is then heated so that the plastic surface melts. Next, the part is integrated in the blow molding process which results in a connection between the pre-fabricated part and the material of the container, similar to that of a plastics welding operation. This particular solution, however, involves an even more complicated manufacturing process than the processes associated with the above described solutions. Furthermore, the above-described problems with respect to the internal pressure resistance and cold flow resistance are also present in this third solution, even despite the reduced permeability attributable to the plastics/metal material combination.
The DE-A 196 27 395 disclosure describes a fuel container, of the general above-identified type, wherein a tubular portion defining a container opening is provided with a flange. The flange forms an abutment surface for accommodating a respective counter-surface of a cover element. The abutment surface of the flange includes an annular groove which receives an O-ring seal. Mounting of the cover element is accomplished by way of a clamping ring which engages behind the flange of the tubular portion. In this way, when the cover element is fully assembled, the cover element is mounted such that it directly contacts the abutment surface of the flange and is supported thereby. The groove in the flange is dimensioned such that the O-ring seal is fully received therein. However, a drawback of this particular solution is that it only provides for axial sealing. Radial sealing under this solution is not provided. In addition, the process of mounting the clamping ring requires skilled personnel because, on the one hand, the selected closing force must be sufficiently substantial so that the respective abutment surfaces of the flange and of the cover element actually engage each other. On the other hand, selecting an excessive closing force may damage the closure system. Furthermore, this particular closure system does not provide for compensation of the setting of the seal, and as a result, permanent permeation resistance cannot be ensured with this closure system.
In view of the above, there is a present need in the art for a fuel container which is manufactured by blow molding in a simple manner, which is easily and reliably assembled by unskilled personnel, and which meets maximal permeability and industry safety requirements.
A cover element and clamping ring are mountable on and sealable to close a tubular portion surrounding an access opening in a wall portion of a container of a fuel tank assembly for a motor vehicle. The tubular portion is contiguous with the wall portion and projects outward from the wall portion so as to define the opening in the wall portion. The tubular portion has a contoured bead which projects radially outward from the projected end of the tubular portion. The cover element is demountably situated on the projected end of the tubular portion and is thereby removably situated over the opening in the container. A sealing ring is removably disposed between the cover element and the tubular portion of the container. The clamping ring is removably snapped onto the contoured bead of the tubular portion of the container. In such a configuration, the sealing ring is cooperatively clamped and sealingly disposed between the cover element, the tubular portion of the container, and the clamping ring whenever the clamping ring is snapped onto the contoured bead of the tubular portion of the container.
In a preferred embodiment of the present invention, the container comprises blow-molded, thermoplastic material. In this way, the contoured bead is preferably made integral with the projected end of the tubular portion, and the tubular portion of the container is preferably made integral with the wall portion of the container. Most preferably, the ratio of the axial length of the tubular portion to the radial thickness of the contoured bead falls within a range from about 1:2 to about 3:1. The sealing ring, in contrast, preferably comprises elastomeric material and is thereby adapted to swell when fuel is absorbed by the sealing ring. Furthermore, the sealing ring preferably has a substantially L-shaped cross-section.
Preferably, the cover element has a cylindrical portion capable of extending into the opening of the container such that the cylindrical portion is coaxially situated within the tubular portion of the container. In addition, the cover element preferably has a flange projecting radially outward from the cylindrical portion. In this way, when the clamping ring is snapped onto the contoured bead of the tubular portion, the sealing ring is cooperatively clamped and sealingly disposed between the cylindrical portion of the cover element, the tubular portion of the container, and the clamping ring. At the same time, the flange of the cover element is cooperatively clamped between the sealing ring and the clamping ring. In a highly preferred embodiment, the cover element includes either a filler pipe for transferring fuel into the container or a fuel pump module with a conduit for transferring fuel from the container.
Further in a preferred embodiment of the present invention, the clamping ring has a lower portion and an inclined surface defined in the inner radial periphery of the lower portion. In this way, the lower portion of the clamping ring can initially slip over the contoured bead of the tubular portion so as to ultimately facilitate the snapping of the clamping ring onto the contoured bead of the tubular portion. In addition, the clamping ring preferably has an annular groove defined in the inner radial periphery of the clamping ring for snapping the clamping ring onto the contoured bead of the tubular portion in a complementary fashion. Further, the clamping ring preferably has a contact surface including a chamfer for cooperatively clamping the flange of the cover element. In this way, when the clamping ring is snapped onto the contoured bead of the tubular portion, the chamfer causes the clamping force applied by the clamping ring to increase when the cover element experiences radial expansion and/or when the sealing ring experiences swelling. Still further, the clamping ring preferably has a cross-section including at least one separation slit defined therethrough. Each separation slit preferably is substantially radially aligned and serves to facilitate the initial slipping of the lower portion of the clamping ring over the contoured bead of the tubular portion.
Preferably, the fuel tank assembly further includes a fastenable strap which removably encircles the outer radial periphery of the clamping ring. The strap serves to secure the clamping ring once the clamping ring is snapped onto the contoured bead of the tubular portion. To accommodate the strap, the clamping ring preferably has an annular groove defined in the outer radial periphery of the clamping ring for matingly receiving the fastenable strap.
To prevent rotational movement, the cover element preferably has an integral projection received in assembly in a complementary recess in the inner radial periphery of the clamping ring.
Objects, features, and advantages of this invention include providing a fuel tank assembly which is simple and economical to manufacture and assemble, has an improved sealing capability that substantially prevents the undesired permeation of fuel and fuel vapors in compliance with industry safety regulations, and is compact, rugged, durable, reliable, of relatively simple design, and in service has a long useful life.